Low carbon steel with titanium aluminum and boron



United States Patent O 3,508,911 LOW CARBON STEEL WITH TITANIUM ALUMINUMAND BORON John Y. Riedel, Bethlehem, Pa., assignor to Bethlehem SteelCorporation, a corporation of Delaware No Drawing. Filed May 11, 1967,Ser. No. 637,617 Int. Cl. C22c 39/02 U.S. Cl. 75-124 7 Claims ABSTRACTOF THE DISCLOSURE A hypoeutectoid boron steel containing small amountsof aluminum, titanium and, optionally, columbium, which is readilyweldable and which can be heat treated to provide a combination of highyield strength and low V-Notch Charpy impact transition temperature andin heavier sections than prior art steels.

BACKGROUND OF THE INVENTION 3,508,91 l Patented Apr. 28, 1970 ice knownhardenability improving constituents from the group consisting ofmanganese, silicon, nickel, and molybdenum and will fall within thelimits shown on Table I. The alloys of this invention do not containsignificant amounts of either chromium or vanadium.

TABLE I Broad Narrow Carbon 10/. 30 12/. 21 Manganese 20/1. 45/. 75Phosphorous. 1 00 Sulphur 05 i 05 'licon 75 Nickel 3. 00 3. 00ChlomiunL. 1 20 1 20 Molybdenum 3. 00 3. 00 Aluminum. .02]. 20 05/. 10Titanium .01]. 04 01/. 03 Columbium 01/. 13 02/. 0 Boron 0005/. 005001/. 005 Vanadium 05 1 Maximum. 2 Optional.

The balance being essentially iron. All compositions are shown aspercentages based on weight.

Table II shows a summary of the yield strength and V15 transverse Charpytransition temperature determinations made on specimens of variousthicknesses of plate steel having compositions within the broad rangesof compositions of Table I. All of the steel plates were heat treated bywater quenching from 1650 F. and tempering at 1200 P. so as to provide amicrostructure which was predominately tempered martensite.

TABLE II Yield Transition Thicknes strength, temp Specimen No. (111.) 0Mn p.s.i. F.

1 M 18 003 107, 000 2 .20 58 003 109,000 l25 .18 59 .004 117,000 4 16 82002 112, 700 A 16 82 002 113,000 155 16 82 002 110, 400 95 16 82 002106, 300 85 19 68 002 116, 350 -70 M 18 55 003 122, 000 -12 5 M 18 58003 113,700 50 M 18 60 004 115, 000 110 1 10 67 003 135, 800 110 2 19.67 003 109,000 2% 19 67 003 101,700 150 2 20 .67 006 106, 300 150ficial elfect on the hardenability of hypoeutectoid boron steels. It isalso known that when these steels have a microstructure which ispredominately tempered martensite they will provide a minimum yieldstrength of approximately 90,000 p.s.i. in sections up to approximately1" in thickness.

SUMMARY OF THE INVENTION It has now been discovered that the addition ofsmall amounts of aluminum and titanium to hypoeutectoid boron steelimproves the yield strength and V15 Charpy transition temperature whenthe microstructure is predominately tempered martensite. These aluminumand titanium additions do not affect the as-quenched hardenability asmeasured by an end quench test, but the improved properties of the steelof this invention are apparent in heavier sections, e.g. 1%" thick oversimilar steels which do not contain aluminum and titanium. It has alsobeen discovered that the addition of a small amount of columbium to theabove hypoeutectoid aluminum, titanium, boron steel will provide eitheran additional increase in yield strength without adversely affecting theV15 Charpy transition temperature or an equivalent yield strength andtransition temperature in even greater thicknesses, e.g. 2 /2" thick.

The hypoeutectoid steel of this invention may contain as much as severalpercent of one or more of the well Specimens 1-7 illustrate theproperties obtained with the heat treated hypoeutectoidaluminum-titanium-boron steels of this invention. Specimens 8-15illustrate the properties obtained with the heat treated hypoeutectoidaluminum-titanium-columbium-boron steels of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT position was produced in theusual manner.

C .12 Si .002 Mn .13 Ni .02 P .012 Cr .04 S .032 M0 .56

2. The melt was blocked by adding spiegeleisen and silicomanganese tothe metal in the furnace.

3. The heat was tapped from the furnace at a temperature of 2890 F. intoa ladle containing sufiicient 50% ferrosilicon to recover approximately.25% silicon.

4. As the heat was being tapped into the ladle addi tions of carbon(coke), aluminum, titanium and ferroboron (13% boron) were made to theladle in that se- The ladle was teemed into ingot molds equipped withhot tops. The ingots were stripped five hours after being poured andheated to 2440-2460 F. for rolling into slabs. The slabs were reheatedto 2350-2400 F. and rolled into plates. Finishing temperatures variedbetween 1870 and 1480 F. Sample No. 8 on Table II shows the compositionand properties of a sample heat treated plate from this heat.

In another specific example a 190 ton heat of steel was produced in thesame manner as the previous example except that the base steel containedapproximately 1.35% nickel and ferrocolumbium was added to the ladleafter the titanium addition and before the ferroboron addition.Specimens 12-15 of Table II illustrate the composition and properties ofsample heat treated plates made from this steel.

The novel steel compositions of this invention can be heat treated to amicrostructure which is predominately tempered martensite in sections upto at least 2 /2" thick so as to provide a weldable steel having minimumyield strength of 100,000 p.s.i. in combination with a V15 Charpytransition temperature not higher than 50 F. in a direction transverseto the major direction of rolling.

In the specific examples the details of methods and the compositions areonly intended as illustrations of this invention which is defined in thefollowing claims.

1. A steel consisting of:

Percent Carbon .10/.30 Manganese .20 1.00 Silicon 10/ .7 Aluminum .02/.20 Titanium .01 .04 Boron .0005 .005

the balance being essentially iron.

2. The steel of claim '1 which also contains .01/ 13% columbium.

3. A hypoeutectoid steel having a microstructure which is predominatelytempered martensite and consisting of:

Percent Carbon (minimum) .10 Manganese .20/ 1.00 Silicon .75 Aluminum.02/ .20 Titanium .O1/.04 Boron .0005/.005

balance essentially iron.

4. The steel of claim 3 which also contains .01/.13% columbium.

5. A steel article having a microstructure which is predominatelytempered martensite characterized by a yield strength of at least100,000 p.s.i. in combination with a V15 transverse Charpy transitiontemperature not higher than 50 F., the said steel consisting of:

Percent Carbon .l2/.2l Manganese .45 .70 Phosphorus (maximum) .035Sulphur do .040 Silicon .20/ .35 Nickel (maximum) 3.00 Chromium do .20Molybdenum do 3.00 Aluminum .05 10 Titanium .01/ .03 Vanadium"(maximum)" .05 Boron .001/ .005

the balance being essentially iron.

6. The steel of claim 5 which also contains .02/ .05

columbium.

7. A steel article having a microstructure which is predominatelytempered martensite characterized by a yield strength of at least110,000 p.s.i. in combination with a V15 transverse Charpy transitiontemperature not higher than 50 F. in sections up to 2 /2" in thickness,said steel consisting of:

Percent Carbon .12/.21 Manganese .45/ .70 Silicon .20/.35 Nickel(maximum). 3.00 Chromium do .20 Molybdenum do 3.00 Aluminum .05/.10Titanium .01/ .03

Vanadium (maximum) .05 Columbium .02/.05 Boron .001/.005

the balance being essentially iron.

References Cited UNITED STATES PATENTS 2,853,379 9/1958 Althouse 1242,858,206 10/1958 Boyce 75126 3,198,630 8/1965 Tarwater 75--1243,288,600 11/1966 Johnser 75126 3,418,110 12/1968 Goda 75-124 HYLANDBIZOT, Primary Examiner UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patent No. 3,508,911 Dated April 28, 1970 Inventor(s) JohnRiedel It is certified that error appears in the above-identified patentand that said Letters Patent are hereby corrected as shown below:

Column 2, Table I, 1ine 10, under the column "Narrow" "phosphorous"should read .05 maximum and not ".00 maximum".

Signed and sealed this 1st day of September 1970.

(SEAL) ATTEST:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR. Attesting OfficerCommissioner of Patents F ORM PO-IOSO (10-69)

